The invention is directed to gelators and their use in gelling a plurality of nonpolar and polar liquids.
Gelation is one of the common forms of colloidal behavior, with gels having been prepared for many substances. A gel is a semisolid system having a high viscosity in the form of a jelly or paste. It is a two-phase colloidal system including a solid and a liquid in more solid form than a sol.
There are at least two general mechanisms of gel formation. The first involves the formation of a gel from an emulsoid. A fluid sol, which includes concentrated droplets of disperse phase scattered throughout a dilute solution of a dispersion medium, is cooled to a point where there is a disturbance of the equilibrium between the droplets and the surrounding dilute solution. The droplets draw the dilute solution into themselves, increase in size, and come into contact with one another forming cells like a honeycomb. This change results in a substantial decrease in fluidity of the sol, which progresses to a sponge-like structure representing a semi-solid jelly, otherwise known as a gel. Continuation of the process results in the viscous particles uniting to form a continuous phase, which encloses the droplets of what was previously the dispersion medium. The structure of the original emulsoid is thereby completely reversed with the more concentrated phase functioning as the dispersion medium, while the more dilute phase is discontinuous.
A second mechanism of gel formation involves the formation of a gel by cross-linking a polymer to form a network in a liquid medium. The liquid prevents the polymer network from collapsing into a compact mass and the network in turn retains the liquid. While some gels are cross-linked chemically by covalent bonds, other gels are cross-linked physically by weaker forces, such as hydrogen bonds and van der Waals forces.
Gelled forms of organic solvents are of particular interest, with attention currently being focused on controlling the flammability of a large variety of organic solvents in order to significantly reduce fire hazard and improve the handling characteristics of the organic solvents.
U.S. Pat. No. 2,388,887 to Weissberger et al. discloses the use of 2-alkyl-substituted 1,4-dihydroxybenzene compounds as agents for producing stiff gels with liquid aliphatic hydrocarbons and liquid halogenated aliphatic hydrocarbons.
U.S. Pat. No. 2,751,284 to Hill et al. discloses "bodying agents" for gelling normally liquid hydrocarbons and other organic liquids. The gelling agents disclosed by Hill et al., are 2-component compositions, the first liquid component comprising an aluminum alkoxide in toluene or other aromatic hydrocarbon of high solvency power, and the second liquid component comprising a mixture of a low molecular weight ketone, water, and C.sub.6 -C.sub.18 fatty acids, preferably isooctanoic acids.
U.S. Pat. No. 3,084,033 to Kelly et al. discloses thickened, normally liquid hydrocarbons which are useful as fuel, as the charge in certain devices such as incendiary missiles, flame throwers, rockets, portable cooling stoves, and the like. The Kelly et al. process comprising mixing the normally liquid hydrocarbons with a very small proportion of solid, crystalline polypropylene. Surprisingly, according to Kelly et al., while propylene functions in the disclosed invention, polymers of other olefins, such as polyethylene and polybutenes were found to be completely ineffective. On the other hand, U.S. Pat. No. 3,507,635 to Sarem discloses gelled jet fuels produced by adding polyisobutylene, the resulting gel capable of being fluidized by high speed shearing, the fluidized gel then being suitable for pumping to a jet engine as a fluid.
U.S. Pat. No. 3,545,946 to Hiatt et al. discloses petroleum distillate fuel compositions in gelled form, the compositions are gelled at room temperature and liquid at elevated temperatures of about 55.degree. C. and above. The gelled compositions comprise 75-95 weight percent of a petroleum distillate fuel and from 5 to about 25 weight percent of a paraffinic hydrocarbon gelling agent containing from about 25 to about 35 carbon atoms per molecule with a melting range of about 140.degree. F. to about 155.degree. F.
U.S. Pat. No. 3,692,504 to Jones et al. discloses the production of gelled compositions containing gasoline and other normally liquid hydrocarbons such as benzene, toluene, xylenes, kerosene, naphthas, and the like, the compositions gelled by a process comprising dissolving a synthetic elastomer in a normally liquid hydrocarbon and treating the resulting solution with sulfur dioxide in the presence of a suitable catalyst, i.e., typically nitrates of the alkali metals, peroxides, hydroperoxides and the like.
U.S. Pat. No. 3,807,973 to Iwama et al. discloses gelled hydrocarbon fuels prepared by gelling the hydrocarbon fuel with a fatty acid diethanolamide, diethanolamine, a fatty acid triethanolamine ester, or a triethanolamine. The compositions purportedly have the advantage that the gelled hydrocarbons are highly stable, have substantially reduced fluidity and still retain their desirable burning quality as fuels for heating means, reciprocating engines, diesel engines, jet engines and the like.
U.S. Pat. No. 3,824,085 to Teng et al. discloses esters of hydroxypropyl cellulose and hydroxypropyl starch useful as gelling agents for organic solvents, the gelling agents particularly useful in gelling methylene chloride (useful in paint stripping) and ethyl bromide (useful in soil fumigants). The hydroxypropyl cellulose laurate derivative is disclosed as particularly useful as a gelling agent for jet fuel.
U.S. Pat. No. 3,960,514 to Teng et al. discloses an improvement upon the invention of Teng et al. ('085, supra) by providing a gelled jet fuel having incorporated therein hydroxypropyl cellulose laurate and an additive comprising an elastic, high molecular weight, synthetic polymer.
U.S. Pat. No. 4,156,594 to Tarpley discloses a thixotropic gel fuel composition comprising 5 to about 75 volume percent of solid carboniferous combustible material suspended in a liquid fuel and about 1 to about 10 weight percent of a substantially completely combustible gelling agent, said combustible gelling agent selected from the group consisting of natural and synthetic gums, resins, modified castor oil polymers and the like.
Other gelling agents have been used for organic liquids as well. U.S. Pat. No. 3,969,087 to Saito et al. discloses the use of a small amount of N-acyl amino acids or derivatives thereof, such as esters, amides, and amine salts of the N-acyl amino acids, as gelling agents for nonpolar organic liquids.
U.S. Pat. No. 2,719,712 to Vaterrodt discloses the formation of gels from solvents such as hexane, heptane, octane terpenes, sesqui-terpenes, benzene, ethyl acetate, and the like, including essential oils for use in the perfume industry. The gelling agent may be lanosterol, which is prepared by saponifying wool greases with sodium hydroxide, thereafter removing the lanoline acids as the insoluble calcium salt, and removing the lanolin alcohols by a suitable solvent such as acetone. The lanosterol is obtained from the lanolin alcohol filtrate by precipitation with acetone and methanol. The gelled hydrocarbons include 8-15% of lanosterol.
Terech, P. et al., J. Physique 46: 895-903 (1985) describes the results of a Small Angle Neutron Scattering (SANS) study of a gel formed by a dilute solution (less than one weight percent solution) of a paramagnetic modified steroid, 3-beta-hydroxy-17,17-dipropenyl-17a-aza-D-homoandrostanyl-17a-oxy in cyclohexane.
Tachibana, T. et al., Bull. Chem. Soc. Jpn. 53: 1714-1719 (1980), describes optically active 12-hydroxyoctadecanoic acids which form thermally reversible gels with aromatic solvents or carbon tetrachloride.
U.S. Pat. No. 4,790,961 to Weiss et al. describes a thermally reversible gel and a method for the formation of gels of certain organic liquids by adding to the organic liquid a gelling agent which is a cholesteryl and cholestanyl ester of anthracene and anthraquinone analogs and derivatives thereof. The mixture is heated until homogeneous and upon cooling a gel is formed. U.S. Pat. No. 5,403,580 to Bujanowski et al. utilize the same or similar gelator as described in U.S. Pat. No. 4,790,961 for gelling organosilicon compounds. The gelation of organosilicon compounds is also mentioned in the patent to Weiss et al. The subject matter of these patents is incorporated herein by reference.
In an article by Lin et al., J. of Amer. Chem. Soc., Vol. 111, No. 15, pp. 5542-51, 1989, cholesteryl 4-(2-anthryloxy)butanoate and related molecules are described as a gelator for organic fluids. These gelators possess a butanoate linking group between the steroidal group in the anthryloxy group. See also Furman et al., Langmuir, Vol. 9, No. 8, pp. 84-88, 1993,and Mukkamala, J. Chem. Soc., Chem. Commun., pp. 375-6, 1995, which also disclose similar gelators.
U.S. Pat. No. 4,174,430 to Kido et al. describes a process for producing porous polystyrene gel by suspension polymerization in an aqueous system. More than 5 mol. % of a radical polymerization catalyst is added to styrene and divinyl benzene in an inert organic solvent. The organo solvent provides the porous nature of the material, which is formed by cross-linking the styrene with divinyl benzene. The porous polystyrene gel is used as a filler for chromatography.
However, in spite of the substantial research conducted in an effort to develop gelled organic solvents, a need has continued to exist for a gelator capable of gelling a wide variety of polar and nonpolar liquids. Moreover, there is a need for highly stable gelled material that is nontoxic and that may be fabricated into a membrane material for filtration purposes and an organic zeolite for control release of various compounds such as medicaments.